Sedimentation tank



Aug. 25, 1936. H. GREEN 2,052,091

VSEDIMENTATION TANK Filed Jan. l0, 1954 2 Sheets-Sheet 1 JNVENTOR. %WHEDE5E N By'aut U7 v r ZTORNEY.

Aug. 25, 1936.

54a ZZ H. R. GREEN SEDIMENTATION TANK' Filed Jaanv 2 Sheets-Sheet 2 W f W x if l INVENTOR.

AT oRNEY Vg y 2 has to be resettled to free it from an excess or' Patented Aug. 2.5,?1936 Tv i sEnnmNfrs'rIoN; fram:

Howard R. Green,

cedar Rapids, its..

Applicants January 1c, 1934, serial no'. 'mausi c] am' s This invention relates-to improvements inl 'sedimentation tanks, and particularly. to-means for assisting in the classiiicatlon process and the withdrawal o! classiiled material from the tank.

usually obtained in sedimentation tanks in which the sludge separates by gravity from the superln atant liquid and from which the sludge and the clar'iiledA liquid are withdrawn independently.

sludge Vfrom the surfaces uponA which lit is. deposited and for moving it to a sump from which it is withdrawn, usually by means of a suction pump. It is the purpose of all such devices to provide for 1 5 also to accomplish this removal with the least possible agitation oi' the supernatant liquid, but' it has been impossible to prevent an undesired amount of lclariiied liquid to be discharged with the sludge and also an undesired amount of sludge to be discharged with the claried liquid. This interferes, in the ilrst instance, with the aftertreatment or digestion of the sludge, sometimes to such an extent that the matter withdrawn supernatant liquid and, in the second instance, it interferes with the emciency ofthe sedimentation process and the after-treatment of the clariiied eilluent. v

By use" of my invention, the sludge is more quickly and completely removed from the tank and'more thoroughly separated `from the superv natant liquid, and these results are accomplished 35 with a greatly reduced mechanical movement,

thereby improving the emciency of sedimentation` and attire same time greatly reducing the quantity oi' power consumed. Moreover, my inven tion'enables the separation to be effected more rapidly with simple and inexpensive installations 'which cover less space than former-apparatus.

In the most common forms oi' plants, concretesettling tanks are provided into which the sewage is introduced. and ln which the solidmatter is permitted to settle to the bottom, and from which it is removed by means of scrapers carried by endless chains or by risid arms which are rotated or otherwise moved over Vthe bottom oi the tank. Ordinarily these scrapers take the form o! wooden scraper nights, blades or bars carried by two `or more endless chains 'which pass around suitable sprockets and are driven by an electric other source oi power. 1 In the devices above described, the sludge 'and sediment must necessarily becar'ried the entire length of the tank 'to the discharge outlet. This procedure has several disadvantages. In lorder to minimize the disturbing effect of the mechanb" cal motion oi' the scrapers, the speed is necessarilyA slow. A considerable period oi time is consumed"4 sedimentation .tank oi .its accumulated sludge 60 In, sewage -disposal plants, clariilcation .is

Mechanical devices are employed for scraping .the

the removal of the sludge with kthe least possiblel 1 amount ciclariiled liquid going out'with it, .and

Vin the passage of one individuali ilight from one end of the settling tank 4to the other. IThe of sludge carried Aby'each scraper is 'therefore the maximum. and they tendencyis to overload the capacity of each scraper.` Lightor ilocculentmaterials or solids which tend? to'g'enerate gases by decomposition are permitted to' accumulate as deposits, for al considerable lapse of timev between thej instant of depositing upon the iloor oi the settling tank -and their ultimate removal at the far end thereof. It must be borne in-mind, in this connection, that the sludge maybe ot a very thin and watery mixture'only slightly heavier than the supernatant liquid, andithat a .relativelyslight disturbance may cause it to rise again orbe dis-i turbed. If -an attempt ris made to remove the @vsludge more rapidly -by speedingjup the's'craping devices, a greater disturbance is created than 'beto reducethe'eiilciencygseptic action,gas'bubblesare formed which clingY l tothe particles of sludge 'andcreate a buoyant eiiect on thecombined particlecausing the vbuh- -ble and its entrained solid-to rise through the supernatant liquid, thereby interfering-with the;

downward travel of settling' particles, and tending to-carry of! an unwarranted` portion of settleableiigndswitn the clarified emuent.

i It is, therefore, a general object o i my invention to avoid the diilicultie's above enumerated and to generally improve the'eillciency of the classiiicaf tion process which takes place in sedimentation tanks of the character described. j'

A more specic object of my invention is to provide means for taking oil! the sludge trom sedi-- mentation tanks at morez frequent intervals than is the usual practice. 1

Another object oi' my inv tion is to v'remove' disturbance thereof.

Another object of my invention is to provide means for Arecapturing sludge-carrying gas bubbles to prohibit theirrise through the super'- natant liquid.` ,y e Another objectief my invention is t'o provide shielding means so arranged as to cut oi! the sludgefromthefsupernatant liquid.

Another object or' my invention is to'provide means for withdrawing sludge from the tank at intervals along th'e iloorof the tank without mav terially disturbing the liquid in the tank. A'Another object of my invention is to'provide' ,g means. for controlling the rate oi.' ow of'sludge as it" is removed from the tank. Another object of my invention is toA provide means for completely clearing the bottomv olthesludge from the supernatant liquidwithout undue without requiring the movement of the scrapers more than a desired fraction of the length of the entire settling tank, thereby providing for a greatly increased rapidity of removal with greatly decreased mechanical movement of the parts of the scraping mechanism and the ,consequent mini num disturbance of the supernatant liquid by the submerged portion of the mecha-i msm.

Another object of my invention is to provide for an efiicient and satisfactory removal of sludge by intermittent operation of the mechanical device, theriy providing for greater periods of quiescence and for more ideal settling conditions,

and also for greatly reducing the power consumed in the mechanical operation.

Another object of my invention is to insure a longer life of the moving parts of the scraping devices, and power units by reason of their operation through a much shorter period of time per day than heretofore required for the scraping operation. i

Other and further features and objects of the invention will be more apparent to those skilled in the art upon a consideration of the accompanying drawings and following specifications, wherein is disclosed a single exemplary embodiment of the invention, with the understanding, however, that such changes may be madetherein as fall within the scope of the appended claims, without departing from the spirit of the invention.

`my invention, together with a portion of the chain for moving the scraper blades, 'a gear for actuating a valve, and a rack attached to the chain for rotating the gear, and

Figure 5 is a view in section of the parts shown in Figure 4, taken along the line 5 5 of the figure.

Referring now to the drawings, there is shown 4at I0 generally.- a tank preferably constructed of concrete or suitable material. 'Ihis tank has end walls II and I2 and side walls I3 and I4 of lthe usual construction, and may be one of aA battery of several tanks having some of the walls in common. C ross braces I5, extending across the tops of the tank, may be used. The tank shown is really in two parts and is divided by centrally locatedparallel walls I6 and I1, although this construction is not necessary, and my inventionmay be incorporated in almost any ferm of tank.

Referring to Figure- 2, I preferably provide a raised platform I8 at` one end of the tank, vupon which a motor I9 and drive gearing 2|, for driving the scraper. belt, may be located.. The floor 22 of the tank is substantially level, with` the exception of a pit or sump 23 and its accompanying outlet 33 at one end thereof of usual construction' 'which may 'be used for collecting and discharging sludge from the tank in connection with the usual installations, or which may be used as an auxiliary to the apparatus, conchannel 3 I structed according to my invention, hereinafter more particularly described.

Sewage flows into the tanks through inlet conduits indicated at 26. The sewage enters a transverse channel indicated at 21 and flows out into the tank over a weir indicated at 23. In the present invention the transverse channel 21 is located inside the conveyor belt which carries the scrapers. A platev 30 preferably depends downwardly inside the tank below the inlet channel 21 to a position just above the lower portion of a chain belt conveyor, hereinafter more particularly described, and separates the main body of the liquid in the tank from the portion in which the conveyor belt travels upwardly, thus preventing disturbance of the main body of liquid by the' upwardly traveling belt.

This location of the inlet channel, and of plate 30, is believed to be novel in the art, and is of major importance because the sewage being clarified does not ordinarily flow into the area through which the rising Scrapers pass, and thereby any remaining solids carried by the Scrapers are prevented from coming in contact with the settling sewage. It is common practice to arrange for a reversal of flow of the sewage entering at 3| and flowing out at 23 or vice versa as desired.

The supernatant liquid or clarified effluent is withdrawn from the tank over a second weir serving the outlet channel 3|. This channel is hereinafter termed the efiiuent channel". It may be seen by inspection of the drawings that the sewage enters at the left or influent channel 21 and flows slowly toward the right or emuent The settleable solids slowly drop out by gravity to the bottom of the tank and are carriedby the Scrapers 32 in a direction toward the influent end of the tank. As soon as any of the Scrapers reach a cross channel 34 the accumulated 'materials carried by the scraper drop into the channel and are withdrawn therefrom as hereinafter described.

The sedimentation tank so far described, with the exceptions above noted, is of the usual construction. In order to provide means for more efficient classification of the materials and for the withdrawal of the sludge without undue withdrawal of supernatant liquid, I prefer, among other expedienx, to withdraw the sludge at certain intermediate points between the ends of the tank. In accomplishing this result, I preferably provide a plurality of cross channels 34 in the floor 22 of the tank. A sectional view of one of these cross channels is shown in Figure 5. The underside of the oor 22 of the tank is preferably provided with depending flange portions indicated at 36 and the channels 34 are formed in the floor and extend downwardly into the anges 36. The channels are preferably formed with semi-cylindrical bottoms, as indicated at 31, and perpendicular sidewalls 38, the

size and shape of the channels being so designed as to satisfy the. conditions in each particular case.v Of courseany suitable shape or size of channel may be employed. The upper edges of the walls of the channel are of bard material or are preferably protected by means of angle irons 39 set in the concrete.

Referring now more particularly to Figures 3, 4 and 5, pairs of plates 4I are fastened to the bottom 22 of the tanks along either side thereof, and a pair of rails 42 are engaged to these plates. A plurality of brackets 43 are disposed on the sidewalls of the tanks, part way up 75 nected by means of plates 4 4, thus providing a pair of supports along the sides of the' walls'of the' tank. Other rails 46` are secured tothe plates 44 and the rails.l 42 and 46 constitute supports for the rollers of the chain belt conveyor. Other ,plates 41 are secured to the side walls of .the tank, and these platesslope outwardly to -ward the center of the tank, so that sludgefsettling-down through the sewage-is directed `toward the center of the tank, in order that it may be carried away by the Scrapers `The plates 41 are braced by means 0.1. Other plates 46..

The rollers 5l which roll on the rails 42 and 46,

fare. flanged, as indicated at 52, in order'that or hood 6I, is secured to the front endof the scraper 66, and extends upwardly and forwardly from theJscraper.

tion and is located infront of the scraper blade above that portion of the blade which first con- -tacts the sludge on the bottom of the tank.' as the scraper moves slowly along,the bottom of the tank. Any gas bubbles or light sludge dislodged by the scraper-and driven upwardly,\ or

rising upwardly, is caught 'by this hood and is either deflected back down toward the bottom of the tank or remains at the upper portion of the hood, on the bottom' side thereof, until-it is withdrawn therefrom as hereinafter explained.

The sera-pers 56 are provided with bracket-4 4angle iron's62, at either end thereof,- and, these angle irons connect the side angle irons 51 at either end thereof. f The end angle irons 62 are provided with upwardly extending portions 63 which are adapted .to be fastened to one of the innermost links 54 as by means of bolts 64. Of course the other end of the. Scrapers are supported from the other chain in the same man-- ner. It isquite apparent that, as the driving motor.2l rotates.' the drive gear 66, the chains 66. carrying the Scrapers 56, move over the drive gear, and outwardly and downwardly into the tank, until they reach an idler gear 61 located near the outer orefliuent end of. the tank. 'I'here these scraper blades come into contact with the floor and start@y their return travel across the, floor, scraping the sludge along before them.-

AThe sludge does not travel the full .length of Y the tank, but need travel only, to the next crosschannel 34 where -it is withdrawn by a. means I am about to describe. The chain and Scrapers,V of course, after they have completed their jours1 ney across the bottom of the tank, move over another idler gear 66 and upwardly to the starting lpoint Aat the Adrive gear 66. The scraperblades, during their travel between' theidler gear 66 and drive `.gear 66, are in a horizontal position, with the hood 6I in a. vertical position to permit thejwitnorawai of gas bubbles, and scouring or cleaning action of thescrapei'- blades Aby their upward `travel through the liquid.

Referring-now more particularly to Figure 31 v y s 2,052,091" .the sides thereof,` and these brackets are con' The hood 6I is preferably curvedover and downwardly at its upper porpreferably provide a conduit, leading through the wall l1 of the sedimentation tank, at each of the crs channels 34. This conduit may beof pipe or any suitable material of any suitable shape,

and is preferably closed off at its outer end, as by means of a plate 12. A valve housing 13 is preferably located at thel inner end of this conduit in such position that the valve within the housing may be rotated by means of a vertically arranged shaft 14. This shaft preferably extends above the upperI edge of the wall of the tank and is rotatably engaged thereto as by`means of a bearing 16. An indicator disk 11 is secured to the bearing 16 and a pointer 16 on the projecting end 'f the shaft 14 sweeps over the disk 11 as the The valve, indicated generally at 13, is adapted tov be intermittently rotated from closed to open positionl and` back to closed position again, by means of a Vrack 19, which is fastened to the link 54a opposite to the-link 54h to which one end,

of the scraper 56`is fastened. A gear 8|, located on the shaft14 in such a position that the gear rack 16 strikes and engages the teeth of the gear as the rack goes by, causes the gear 6l to berotated through one-half of a revolution eachtime a rack portion goes by.

The valve 13 is connected with a pipe 62, which passes through the wall 12, and which is in turn connected with a second valve 83 on the outside of the tank. This valve 63 may be termed th volume of ow" control valve, and it may be opened and closed as desired to regulate the volume ofl sludge drained off from the tank each y -or pipe line as desired. A small tube 66 is prefer-4 {ably provided for conveying lubricant to the valve 13, or a hollow stem and hollow shaft 14]- may be provided for lubrication from above. The tube 66 is, of course, connected with the interior of-the valve 13, as indicated in the drawings. passes through the wall 12, and has aiitting 61 at its outer end so that lubricant may be supplied to the valve 13 without removing it from the tank, and the same principle would b e applied if the hollow stem type is utilized. It is apparent that the valve 13 may be'removed from the tank for inspection and repairs by removing the plate 12. It is obvious of course that the construction just described is duplicated at all of the cross channels 34;

In-operation of the device, as the Scrapers 56 scrape along the bottom of the tank, they collect material from the bottom thereof, as has been described. This material is carried along until it reaches one of the cross channels 34, where it falls into the cross channel. The scraper proceeds across the top of the channel 34 and after the leading edge has reached the other'side of the channel, the rack 19 begins to engage the teeth of the gear 6| to open the valve 13. As the chain 56 proceeds, the` v`alve 13 is opened to its fullest so positioned as to cause opening of the valve 13.

before the; leading edge 56a of the scraper 56 reaches the wall 39a, so that any material which has gathered -in front-of the scraper and which may not have fallen into the channel 34 may be drawn into the channel.

During the period when the scraper 58 is over the channel 34, the rubber or composition flap 58 eiIectively closes the top oi' the channel. Liquid from within the tank thus is forced into the far end 34a of the channel 34 and drives the sludge in the channel 34 through the valve 13 where it is discharged to the sludge channel or pipe line 84.

The valve 83 may be so regulated that a minimum may enter the channel by flowing in under the angle iron 48 at the inlet or far end of the cross channel.

By use of any suitable time clock control known to the art, it is possible to stop the mechanism for any desired period ofA time, as soon as the discharging operation has been completed, thereby permitting the material in the tank to lie, in a quiescent` condition, so far as mechanical movement is concerned, until the mechanism is again set in motion. It is obvious that this operating cycle can be varied atwill until optimum conditions are determined. It is also obvious, by way of example, that if there be six cross channels, that the entire floor area of the tank will be swept free from sludge and the sludge discharged, when any one flight has traversed one-sixth of the length of the tank, and it likewise follows logically that the units described, when operating at the same speed as present units, will accomplish the same result with one-sixth of the mechanical motion. one-sixth of the wear on moving parts, and one-sixth of the power consumption. Similar ratios would hold good for any givennumber of cross channels.

It is apparent that the sludge may be` removed at frequent intervals by means of a device constructed according to my invention. Regulation of the amount of sludge removed may be accurately controlled by the valves 83. For instance, the valve 83 controlling the flow of fluid from channel 34a may be open only to a small degree, inasmuch as the major part of the separation of the sludge may have occurred at the inner end of the tank. The other valves may be successively opened to a greater extent so that agreater volume of flow occurs at each successive valve or cross channel. The racks J9 may be so located on the chain 50 that any successive opening or sequential opening of valves 13 may be secured, or opening of all the valves at one time may be effected. The positions of the racks 19 on the links 54 may be so regulated, as has been explained, that opening of the valve 'I3 occurs before or after the channel has been closed by the scraper 56. If desired, the trailing edge of the scraper might be cut at an angle so that influx of the supernatant liquid into the channel back of the scraper blades, while the valve 13 wasstill open, might be secured and the flow of liquid thus regulated.

It is apparent that the principles of my invention are applicable regardless of the directionof ilow of the sewage through the tank, and that the introduction of the inflow of sewage at the center line or other points in the tank, with the effluent channel at either or both ends, would not materially affect the operation of devices con-yv tomy invention may be used or modied for use l departing from the spirit andscope of my in vention as set forth in the appended claims.

I claim as my invention:

1. In a sedimentation tank of the type in which Scrapers pass over thebottom thereof to collect material from the b'ottom of the tank, means for improving the eiiiciency of the classication process comprising horizontally-extending flaps on the Scrapers, the floor having channels therein adapted to be intermittently covered. by the scraper flaps, valve means for withdrawing material from the channel, and means associated with the scraper blades for opening and closing the valves at predetermined times.

2. In a sedimentation tank, an endless belt, Scrapers on the belt, valves for withdrawing liquid 'from the floor of the tank, and means on the endless belt for periodically opening and closing the valves.

3. In a sedimentation tank, an endless belt, Scrapers on the belt. valves for withdrawing liquid from thefloor of the tank, and means on the endless belt for periodically opening and closing the valves in consecutive order.

4. A sedimentation tank having a plurality 'of' cross channels in the tloor thereof, scraper blades adaptedto scrape material into the cross channels, means on the scraperblades forfclosing the cross channels' as the scraperl blades pass alongthe floor, .valves adapted to control the flow oi' fluid from the cross channels, and means associated with the scraper blades and channel closing means for opening and vclosing the valves during the'time they are covered by the channel closing means.-

5. In a sedimentation tank, a scraper blade for scraping material from the bottom of the tank, and means attached to the front of the blade for capturing gas bubbles which rise'through the supernatant liquid in front of the scraper blade.

6. In a sedimentation tank, a scraper adapted to pass along the bottom of the tank, means for capturing gas bubbles `rising from the bottom of the tank byreason of the passage of the scraper,

and means for moving the capturing means to one end of the tank and discharging the gas bubbles at that point so that they will not disturb the main body of supernatant liquid.v

7. A sedimentation tank having a plurality of cross channels in the floor thereof, tracks on the opposite side walls of the tank, endless chain belts adapted to ride on the tracks, scraper blades extending between-the chain belts and adapted to scrape material from the oorof the tank into the crosschannels, means on the scraper blades for closing the" cross channels after thei scraper blades have crossed over them, valve means4 

